An aircraft engine emulator comprises a housing; at least one actuator or emulated actuator disposed within the housing; at least one sensor or emulated sensor disposed within the housing; and a wired connection configured to connect the at least one actuator or emulated actuator and the at least one sensor or emulated sensor for communication with components on board an aircraft, wherein the aircraft engine emulator is configured to take the place of an engine to the components on board an aircraft that has at least one missing or non-functional engine.

Examples are disclosed that relate to virtual semiconductor fab environments. One example provides a method of monitoring a process performed on a substrate in a processing tool. The method comprises obtaining runtime data from sensors of the processing tool while running the process in the processing tool. The method further comprises performing a runtime simulation by simulating a digital twin using the runtime data and a recipe for the process. The method further comprises receiving a selection of a spatial viewpoint within the digital twin of the processing tool. The method further comprises rendering an image of a virtual state of the processing tool using the runtime simulation and the spatial viewpoint, and outputting the image of the virtual state.